New light mediators and the neutrino fog: Implications from XENONnT nuclear recoil data

Current ton-scale, xenon-based dark matter (DM) direct detection experiments have now reached the sensitivity required to observe solar neutrinos, marking the onset of the so-called neutrino fog. In this work, we explore how this fog is modified when either neutrinos or DM interact with nuclei through a new scalar, vector or axial-vector interaction, considering both heavy and light mediators. Using the latest nuclear-recoil data from XENONnT, which show indications of coherent elastic neutrino-nucleus scattering from $^8$B solar neutrinos, we derive new strong bounds on couplings of light mediators. We find that these limits are significantly more stringent when the mediator couples to DM, rather than when new physics affects only neutrino interactions. Building on these results, we recompute the expected neutrino fog and compare it with the corresponding constraints on spin-independent and spin-dependent DM-nucleon interactions. We show that the morphology of the neutrino fog can be markedly modified if either neutrinos or DM interact with nuclei through light mediators, even in light of these recent constraints.